There are several reports of the reaction of individual alkali metals with trialkylaluminum compounds to form the corresponding tetraalkylaluminates as their alkali metal salts, particularly from either sodium metal or potassium metal. The reaction between an alkali metal and a trialkylaluminum compound is often represented as:3M+4AlR3→3M[AlR4]+Alwhere M is the alkali metal and R is an alkyl group. See for example L. I. Zakharkin and V. V. Gavrilenko, Journal of General Chemistry of the U.S.S.R., 1962, 32, 688; and E. Schaschel and M. C. Day, J. Am. Chem. Soc., 1968, 90, 503. Mixtures of alkali metal salts, particularly sodium and potassium, of tetraalkylaluminates have been reported and used. See for example U.S. Pat. No. 3,234,115 and U.S. Pat. No. 3,969,195. Another way of naming an alkali metal salt of a tetraalkylaluminate is as an alkali metal aluminum alkyl, for example, sodium aluminum tetraethyl, which is synonymous with sodium tetraethylaluminate.
One reference to sodium potassium alloy in connection with a tetraalkylaluminate is found in U.S. Pat. No. 3,285,947, issued to Ziegler and Lehmkuhl, from column 1, line 71 to column 2, line 6, which describes a reaction of sodium tetraethylaluminate to form potassium tetraethylaluminate, and states                When stirring [sodium tetraethylaluminate] with metallic potassium, sodium will be liberated. The latter forms an alloy with potassium and the result hereof is that finally hardly more than 80 mol percent of potassium compounds in addition to 20 mol percent of sodium compound are present in the final product. Moreover, the establishment of equilibrium which is obviously present takes an extended period of time.This disclosure, however, is non-enabling for efficient production of tetraalkylaluminates as mixtures of their sodium and potassium salts. No further information is given regarding the solvent used (or lack thereof); what temperatures, if other than room temperature, were employed; what other pertinent conditions, if any, were used in attempting the reaction described; or how long it takes for the equilibrium to be established. On the other hand, this description does make clear that some sodium potassium alloy remains in the reaction mixture at the end (because the reaction does not proceed to completion), an undesirable result for Ziegler and Lehmkuhl because 100% yield of the potassium salt was desired, in addition to the presence of the remaining sodium potassium alloy. Additionally, U.S. Pat. No. 3,285,947 also discloses at column 1, lines 55–62, that in the reaction 3K+4AlR3→3K[AlR4]+Al        Potassium aluminum tetraethyl produced in this manner has been found to contain always certain impurities which can be removed only with great difficulties by recrystallization. The raw product of this reaction is brown-colored and can hardly be obtained completely colorless by the purification.Thus, U.S. Pat. No. 3,285,947 teaches away from reacting potassium metal with trialkylaluminum compounds to obtain potassium tetraalkylaluminates because of the concurrently-formed, persistent impurities.        